Thrust bearings for underground drilling engines

ABSTRACT

The oil bath layout for the lower thrust bearing in an underground drilling machine comprises an upper sealing joint below which means are provided for maintaining the oil pressure at a level which is at least equal to that of the surrounding pressure of the mud in the borehole. Such means may include a cylinder fitted with a piston and having one of its chambers in communication with the oil bath and the other of its chambers in communication with the borehole. An oil pressure control spring is located in the chamber in communication with the borehole and acts on the piston. The upper sealing joint forms the lower end of a second chamber in communication with the borehole and closed at its upper end by a leak limiting joint, such as one of the labyrinth type.

United States Patent Dicky [151 3,659,662 1 May 2,1972

[ THRUST BEARINGS FOR UNDERGROUND DRILLING ENGINES [2]] Appl. No.:30,803

3,365,202 l/l 9 68 Carleton l 75/l07 X FOREIGN PATENTS OR APPLICATIONSl,l95,283 5/1959 France l 75/107 1,923,282 5/1969 Germany 1 75/107Primary Examiner-David H. Brown Attorney-Sylvester J. Liddy, John .1.Hart. Joe E. Daniels and Charles E. Baxiey [57] ABSTRACT The oil bathlayout for the lower thrust bearing in an underground drilling machinecomprises an upper sealing joint below which means-are provided formaintaining the oil pressure at a levelwhich is at least equal to thatof the surrounding pressure of the mud in the borehole. Such means mayinclude a cylinder fitted with a piston and having one of its chambersin communication with the oil bath and the other of its chambers incommunication with the borehole. An oil pressure control spring islocated in the chamber in communication with the borehole and acts onthe piston. The upper sealing joint forms the lower end of a secondchamber in communication with the borehole and closed at its upper endby a leak limiting joint, such as one of the labyrinth type.

5 Claims, 2 Drawing Figures TIIRUST BEARINGS FOR UNDERGROUND DRILLINGENGINES THE INVENTION This invention relates to underground drillingengines, such as electric drilling machines, volumetric hydraulicengines, turbo-drills and the like, and more particularly to an improvedthrust bearing for such type of drilling engines.

Drilling machines of the indicated type may be fitted with radial oraxial bearings housed in lubricating oil baths. In such constructions,the oil housing must be isolated by suitable sealing means from thesurrounding areas which are filled with drilling mud. A current methodof so sealing the oil housing for a lower thrust bearing running in anoil bath, is to locate between the upper and lower sealing joints of thehousing, a device for maintaining the oil in the housing at a pressurewhich is never lower than that in the borehole of the well. This deviceis composed of a cylinder fitted with a piston and having one of itscylinder chambers connected with the oil-filled area of the housingwhile the other chamber thereof is in communication with the borehole.An oil pressure setting spring is mounted in the chamber which is incommunication with the borehole and this spring acts on the piston. Ithas been found that this lay-out has the drawback that in operation itcauses the two sealing joints of the oil housing to be subjected togreat differences in pressure. Thus, the upper sealing joint of thehousing is subjected to the high pressure of the drilling mud before itpasses through the unit, while the lower sealing joint thereof issubjected to a far lower pressure, that of the borehole at the outlet ofthe drilling tool. Under such conditions, dependent on whether the oilpressure in the thrust bearing is set at a level above or below that ofthe pressure of the drilling mud acting on the upper sealing joint,there may occur, due to the aforesaid great differences in the pressuresapplied to the sealing joints; either an oil leak from the bearingthrough the lower sealing joint, or a penetration of the drilling mudinto the bearing through the upper sealing joint.

It is the primary purpose of the present invention to improve this typeof device so to avoid the above discussed drawback. Essentially this isaccomplished in accordance with the invention by providing a chamber incommunication with the borehole of the well above the upper sealingjoint and isolating such chamber in its upper area from the highpressure drilling mud passing through the unit by a leak limit joint(for example) of the labyrinth type. As a result of such construction,both sealing joints are subjected to the pressure of the borehole andany penetration of drilling mud into the thrust bearings can beprevented by slightly overpressurizing the oil in the thrust bearing,without risking oil leaks.

In order that a better understanding of the invention may be obtained,reference is made to the following description of a conventional lay-outconstruction fitted to a turbo-drilling machine as an example of themanner in which the invention may be practiced and to the accompanyingdrawings in which:

FIG. 1 is an axial section view of a conventional lay-out of thrustbearings such as used with a turbo-drilling machine; and

FIG. 2 is an axial section view showing how the improve ment of thisinvention may be incorporated in the lay-out illustrated in FIG. 1.

The conventional turbo-drilling machine shown in FIG. 1 of the drawings,comprises a static body indicated generally by the reference numeral 1,and enclosing a rotating drill shaft generally designated and driven bythe turbine blades, not shown, as is usual. The turbine, as iscustomary, is driven by drilling mud which enters into an annular space11 between the body 1 and the shaft 10 after passing through the outletof the turbine blades. The drilling mud passes through openings 12 boredin the shaft 10 into a barrelling 13 formed in the lower portion 14 ofshaft 10 and then flows downwardly through such barrelling. From there,the mud penetrates the drilling tool, not shown, which is screwed to thelower end of the shaft portion 14, and passes from such tool into thewell to flow upwardly through the annular space 15 formed by the borebetween the well wall 16 and the body 1 of the turbine drilling machine.7

The body 1 of the drilling turbine includes two lower parts-2 and 3which are assembled in threaded relation as indicated. Formed in thespace-between such body parts 2, 3 and the portion 14 of the shaft 10 isan oil bath 20 which is isolated from the mud by an upper sealing unit21 and a lower sealing unit 22, both of usual construction. In the oilbath 20 housed by the body parts 2, 3, the rings mounted on the shaftportion 14, and the sealing units 21, 22, are containedthe radialbearings 23 for supporting the shaft 10 in the body 1 of theturbo-drilling machine, and the ball thrust bearings 24 whichtransmitthe longitudinal dynamic stresses of the shaft l0 through to the body 1.a

When the turbo-drilling machine is lowered into the bore 15, thehydrostatic pressure of the mud increases with the depth, andaccordingly, there arises the risk that excessive dynamic stresses maybe impressed on the oil housing sealing units 21 and 22. In an attemptto avoid this condition, there is utilized a unit of known constructiondesigned to compensate for the hydrostatic pressure on the oil bath 20.As shown in FIG. 1 this unit comprises a cylinder 26 mounted between thebody parts 2, 3 and a piston 27 slidable in such cylinder and providedwith sealing joints 28. The piston 27 bears on a spring 29 seated on anexternal flange 30 by which the cylinder 26 is mounted on the body parts2, 3. An opening bored in the lower body part 2 connects the area incylinder 26 where the spring 29'is mounted with the drilling mud whichfills the-borehole 15. Thus, any variations in the hydrostatic pressureof the liquid in the borehole 15 are transmitted through piston 27 tothe oil bath 20 between the sealing units 21, 22. The additional forceof the spring 29 on the piston 27 ensures that the pressure on the oilwill be greater than the mud pressure at the exterior of theturbo-drill. In the event of slight leaks of oil through the sealingunit 22, the oil would escape through the body 1, but the mud would notpenetrate through the sealing unit 22 into the oil bath. Any lowering ofthe volume of the oil bath 20, due to such leaks will be automaticallycompensated for by the movement of piston 27 under the pressure ofspring 29. This system however, has an important drawback resulting fromthe great difference in the mud pressure between the area 11 above thesealing device 21, and that of the mud in the area around theturbo-drill whose pressure acts on the sealing device 22. Thisunavoidably leads to the condition that the pressure in the oil bath 20is lower than that of the mud in space 11. There is thus the choice ofchancing the increased risk of mud penetrating into the oil baththroughsealing device 21, or of increasing the strength of the spring 29 tomake the oil pressure greater than that of the mud in area 11. In eithercase, however, the resultant difierence in pressures on either side ofthe sealing device 21 is liable to be excessive and of such extent as tocause an unacceptable degree of oil leaks. This situation cannot becorrected by linking the area in cylinder 26 containing the spring 29with area 11 instead of with the area 15 surrounding the machine, sincealthough the spring force could be reduced, an excessive pressure wouldstill be exerted permanently on the oil bath 20. In fact, the pressuredrop of the mud through drilling tools such as diamond bits andparticularly toothed wheels known as jets" is of such extent, that thepressure difference between the oil and the drilling mud may reachseveral decabars and may even exceed l hectobar, which exceeds thetolerances of the rotating sealing joints used in current practice. 7

FIG. 2 of the drawings illustrates how the aforesaid drawbacks in thelay-out of FIG. 1 can be overcome by modifying such structure inaccordance with the invention. In considering FIG. 2, it will beunderstood that the lower part of the turbine situated below the uppersealing unit 21 and not shown in such figure, is identical to that shownin FIG. 1 of the drawings and above described. The upper sealing unit 21in the construction of FIG. 2 closes the lower end of an annular space40 formed between the machine body 1 and a ring 41 mounted on the lowershaft portion 14. This area or space 40 is in communication with thewell space surrounding the machine through openings 42 bored in thebody 1. A sealing unit generally designated 43 is mounted on the body 1and the lower shaft portion 14 and separates the space 40 from the space11 which is filled with the drilling mud under pressure dischargedthereinto by the turbine blading. The sealing unit 43 is of thelabyrinth type customarily used in turbo-drilling machinery and iscomposed of piling parts 44 mounted on the shaft portion 14 between thering 41 and a circular shoulder 45 formed .on such shaft portionadjacently below the openings 12 therethrough. The sealing unit 43 isalso composed of piling parts 46 mounted in an internal groove 47 formedin the inner wall of the body 1. The parts 44, 46 are so dimensionedthat the play between the parts 44 and the parts 46 is very low. Theform of the sealing parts 44' and 46 which are made integral with theparts Y44 and 46, respectively, is such that a complex flow line isimposed on the drilling mud and they vary considerably in section insuch manner that the resistance to the flow of mud along such flow lineis considerable. As a result of this construction mud leaks are limitedto a technically acceptable flow level. The flow line formed by thesealing parts 44, 44, 46, and 46 is in communication with the chamber orspace 40 through an annular opening 48 in the upper end of such chamber.

It will be understood from the foregoing discussion, that as a result ofthe construction of the turbine according to the invention, the annularspace 40 above the sealing unit 2lis subjected to the pressure of themud which fills the borehole 15, thereby subjecting both sealing units21, 22 for the oil bath to the pressure existing in theborehole 15.Thus, the inherent drawbacks in known layouts of the type shown in FIG.1 are avoided. By choosing a suitable strength for the spring 29 so thatthere is ensured a slight overpressure of the oil in the thrust bearingscompared with the pressure of the mud in the borehole 15, allpenetration of the drilling mud in the chamber 11 into the thrustbearings may be avoided without causing oil leaks.

What is claimed is:

1. An underground drilling machine having a static body enclosing arotating drill shaft provided with a barrelling through which fluidpasses from a space containing such fluid under high pressure to thedrilling tool of the machine and having between such static body anddrill shaft an oil bath housing for a bearing positioned adjacent saidfluid space, said housing including an end sealing joint between the oilbath therein and said fluid space, a cylinder having a piston formingthe area thereof into two chambers, one of said chambers being incommunication with the oil filled area in said housing, and the other ofsaid chambers being isolated from such oil filled area and incommunication with the exterior of said machine so that external fluidpressure is exerted on the oil bath in said housing and on one side ofsaid end sealing joint, said end sealing joint forming one end of athird chamber in communication with the exterior of said machine so thatexternal fluid pressure is exerted on the other side of said end sealingjoint, 1

and a second sealing joint between said third chamber and said fluidspace, fonning the other end of said third chamber, and isolating saidthird chamber from said fluid space.

2. An underground drilling machine as defined in claim 1 in which saidsecond sealing joint is a leak limiting joint having a flow path incommunication with both the fluid space and said third chamber.

3. An underground drilling machine as defined in claim 1, in which saidsecond sealing joint is a leak limiting joint of the labyrinth type.

4. An underground drilling machine as defined in claim 1, including anoil pressure control spring in said other chamber and acting on saidpiston to provide in the oil and on said one side of said end sealingjoint a slight overpressure compared with the external fluid pressureexerted on the other side of said end sealing joint.

5. An underground drilling machine as defined in claim 1 in which saidhousing is positioned below a fluid space containing drilling mud underhigh pressure, said end sealing joint thereof forms the upper sealingjoint for the oil bath in said housing, said cylinder is contained insaid housing and constructed so that said other chamber thereof isisolated from the oil filled area of said housing by said piston, and anoil pressure control spring contained in said other chamber and actingon said piston, so that there is provided in the oil and on said oneside of said upper sealing joint a slight overpressure compared with thepressure on the other side of said upper sealing joint.

1. An underground drilling machine having a static body enclosing arotating drill shaft provided with a barrelling through which fluidpasses from a space containing such fluid under high pressure to thedrilling tool of the machine and having between such static body anddrill shaft an oil bath housing for a bearing positioned adjacent saidfluid space, said housing including an end sealing joint between the oilbath therein and said fluid space, a cylinder having a piston formingthe area thereof into two chambers, one of said chambers being incommunication with the oil filled area in said housing, and the other ofsaid chambers being isolated from such oil filled area and incommunication with the exterior of said machine so that external fluidpressure is exerted on the oil bath in said housing and on one side ofsaid end sealing joint, said end sealing joint forming one end of athird chamber in communication with the exterior of said machine so thatexternal fluid pressure is exerted on the other side of said end sealingjoint, and a second sealing joint between said third chamber and saidfluid space, forming the other end of said third chamber, and isolatingsaid third chamber from said fluid space.
 2. An underground drillingmachine as defined in claim 1, in which said second sealing joint is aleak limiting joint having a flow path in communication with both thefluid space and said third chamber.
 3. An underground drilling machineas defined in claim 1, in which said second sealing joint is a leaklimiting joint of the labyrinth type.
 4. An underground drilling machineas defined in claim 1, including an oil pressure control spring in saidother chamber and acting on said piston to provide in the oil and onsaid one side of said end sealing joint a slight overpressure comparedwith the external fluid pressure exerted on the other side of said endsealing joint.
 5. An underground drilling machine as defined in claim 1,in which said housing is positioned below a fluid space containingdrilling mud under high pressure, said end sealing joint thereof formsthe upper sealing joint for the oil bath in said housing, said cylinderis contained in said housing and constructed so that said other chamberthereof is isolated from the oil filled area of said housing by saidpiston, and an oil pressure control spring contained in said otherchamber and acting on said piston, so that there is provided in the oiland on said one side of said upper sealing joint a slight overpressurecompared with the pressure on the other side of said upper sealingjoint.